Biology I BIO 103 HbR

The Human Digestive System Anatomy Digestive system Structural Regions Digestion Why chemical digestion is needed? How Does Chemical Digestion Occur? Digestion in different stages

Digestive System Digestive system consists of series of connected organs whose purpose is to break down, or digest, the food we eat. Food ( large complex molecules)simple and smallest parts absorbed in bloodstream Digestion generally involves 2 stages: Mechanical Digestion Chemical Digestion

Why is Chemical Digestion Needed? Chewing, chopping and mixing with saliva can only split up the food into small pieces. Foods need to be separated into small and simple molecules to be effective. Nutrients are absorbed by blood through the cell membrane and blood transport them to different parts of the body. Fats and Carbohydrates are water insoluble. They are converted to a soluble product before they are absorbed. Finally, Carbohydrate, Fat and Protein that we eat are not the same as our own Carbohydrate, Fat and Protein. Digestive system converts those “animal/plant” products to “Human products”.

How Does Chemical Digestion Occur? Most chemical digestion in your body uses a water molecule to break the bonds between the parts of the large molecules. This process is called hydrolysis. Specific enzymes may speed up the hydrolysis of the large molecules by positioning the water molecule in just the right place for the chemical reaction to occur. For example, proteinases or proteases help hydrolyze proteins, lipases help hydrolyze lipids or fats, and carbohydrases help hydrolyze carbohydrates.

Anatomy 1. 2. 3. Accessory Digestive Organs 1. Salivary Glands 4. 5. 6. Anal Region Accessory Digestive Organs 1. Salivary Glands 2. Pancreas 3. Liver 4. Gallbladder

The Mouth Region Mechanical and Chemical Digestion Glands in cheek secrets saliva (digestive enzymes). Make the food chopped, moist and smooth for easy swallowing. Food enters in pharynx (food and air passageway). Epiglottis covers the trachea(windpipe) when food is swallowed. Sense receptors in mouth can characterize the food texture, temperature and taste. Amylase; an starch/carbohydrate digesting enzyme is secreted from mouth.

The Mouth Region Your mouth produces up to 1.5 liters of liquid every day Saliva is produced when food being tasted or chewed Saliva is a solution of three main substances: Water: for moisten and taste Amylase: Breakdown of starch/Carbohydrates. Mucin: Lubricant the food

The Esophagus The esophagus is a muscular tube about 25 cm (10 inches) and 2.5 cm (1 inch) across long, passes behind the trachea (windpipe) and heart and penetrates the diaphragm (muscular wall between the chest and abdomen) before reaching the stomach within two to three seconds. Digestion by rhythmic muscle contractions (tightening) known as peristalsis. No chemical digestion.

The Stomach located in the upper abdomen just below the diaphragm sac-like structure with strong, muscular walls The stomach can expand significantly to store all the food from a meal both mechanical and chemical processing contracts about three times per minute, churning the food and mixing it with gastric juice. thousands of gastric glands (2 liters of gastric juice/day )in the lining of the stomach, consists of water, hydrochloric acid(HCl), an enzyme called pepsin, and mucin (the main component of mucus)

The Stomach Composition of Gastric Juice: Water food moisten and dissolves any soluble nutrients HCl (Hydrochloric Acid) It helps dissolve insoluble minerals. It kills many bacteria taken in with the food. It aids in the digestion of starch. It provides the acidity needed to keep the pepsin enzyme working. Pepsin Pepsin, a protease enzyme, Hydrolysis of a protein by pepsin produces several shorter chains of amino acids. Mucin coats the stomach, protecting it from the effects of the acid and pepsin About 4 hours after each meal, small portion of processed food is passed through “pyloric sphincter” to duodenum (first part of small Intestine).

The Small Intestine Most digestion, as well as absorption of digested food, occurs in the small intestine. This narrow, twisting tube, about 2.5 cm (1 in) in diameter, fills most of the lower abdomen, extending about 6 meters (20 feet) in length. Three parts: Duodenum Jejunum Ilium Chemical digestion takes place in small intestine by digestive juices from 3 different sources: Liver The Pancreas Intestinal Lining

The Small Intestine Liver: Pancreas: produces 3 enzymes: makes complex mineral salts in a solution called bile stored and concentrated unit needed in the gall bladder. Bile salts break up large drops of fat into many smaller droplets. Bile salts also prevent the small droplets from going back together again. It stores glucose in the form of starch-like molecules called glycogen. Pancreas: produces 3 enzymes: Protease, which hydrolyze protein. Amylase, which hydrolyze starch, and Lipase, which hydrolyze fat or oil Intestinal Lining: Produces enzymes to make the small chains of foods(proteins/carbohydrates) into smallest parts. Mucin lubricates and protects the wall of Intestine.

The Large Intestine A watery residue of indigestible food and digestive juices remains unabsorbed They leaves the ileum of the small intestine and moves by peristalsis into the large intestine, where it spends 12 to 24 hours The large intestine is 1.5 to 1.8 meters (5 to 6 feet) long and about 6 cm (2.5 inch) in diameter. Function: It absorbs water—about 6 liters (1.6 gallons) daily Absorbs dissolved salts. bacteria in the large intestine promote the breakdown of undigested materials Bacteria make several vitamins, notably vitamin K, which the body needs for blood clotting. large intestine moves its remaining contents toward the rectum, which makes up the final 15 to 20 cm (6 to 8 in) of the alimentary canal The rectum stores the feces—waste material that consists largely of undigested food, digestive juices, bacteria, and mucus—until elimination.

Anatomy 1. 2. 3. Accessory Digestive Organs 1. Salivary Glands 4. 5. 6. Anal Region Accessory Digestive Organs 1. Salivary Glands 2. Pancreas 3. Liver 4. Gallbladder

At A Glance… Food Type Major Digestion area Major Digestive Enzyme End products Carbohydrates Mouth Amylase Glucose Protein Stomach Pepsin Amino acids Fats Small Intestine Lipase Small lipid molecules

Thank you ….any questions?

Appendix (for MID-2 review) Flagella